In Overwatch, each character has a series of prerecorded voice lines that players can deploy at will during matches. These include everything from greetings and taunts to McCree's notoriously Kirk-Hamilton-irritating "I'm your Huckleberry." It isn't hard to spam them. Just because you can, however, does not mean you should.
In a recent Overwatch forum post, one player complained that they'd been unjustly silenced - that is, had their communication functionality disabled - on multiple occasions. In response, principle designer Scott Mercer pulled up records of the player's grievances and specifically noted that, even without a microphone, this player had been "spamming voice lines" in addition to being a poor sport, killing themselves, and generally being a nuisance.
The voice lines thing caught other players' attention, because it isn't uncommon for folks to make characters babble out greetings and whatnot like their motormouths have caught fire. It's usually in good fun, though.
"You can get SILENCED for Voiceline spamming?????" wrote one player, summing up others' concerns.
Mercer went on to clarify that voice line spam is only a problem when it interferes with other players' ability to enjoy themselves.
"Abusive Chat is any form of hateful, discriminatory, obscene, or disruptive communications," Mercer wrote. "Threatening or harassing another player on either team is also unacceptable, regardless of the words used. So YES, if you spam character voice lines in a way that is either disruptive or would be considered harassment, then you could be actioned."
Some players seem to regard this as the advent of some totalitarian voice line monitoring regime, but I imagine the bulk of players who spam the odd quote here and there for a laugh will never get any Blizzard-branded grief for it. In this case, especially, it seems like voice line spam was an extension of other, more overtly abusive behaviours. In Overwatch as in life, don't be a dick and you'll probably be fine.
Unless you're a Genji who spams "I need healing" all the time. Then you deserve whatever terrible fate befalls you.